For many applications in materials and bioscience research, spatially resolved spin resonance detection with high sensitivity is desired. Conventional spin resonance detection experiments are usually performed by placing a sample in a microwave cavity or a pair of RF coils situated in a strong DC or substantially static magnetic field that is perpendicular to the microwave or RF magnetic field. High power microwave or RF radiation excites the coherent spin precession. Precessing spin-induced induction and absorption signals are picked up by cavity or coil and detected by diode mixer. Although the intrinsic sensitivity is limited by cavity Johnson noise, which is near single-spin detectivity, this level of detection has never been possible practically. Primary limitations in a conventional experiment are large background noise from high power excitation signal generated by high-power klystron source (need to excite spin in bulk samples) and diode detector noise since low noise amplifier cannot be employed before diode detector without being saturated by high level excitation signal pick up at detection port.
What is needed is an approach that provides spin resonance detection, preferably spatially resolved to within 0.5 μm to 1 mm. Preferably, the approach should avoid detection of background signals, such as the strong input or excitation signal, and should not require use signal levels that are at or above a saturation threshold.